The present invention broadly relates to baghouse filtration systems. Specifically, the present invention is a Process and Apparatus for Rejuvenating Baghouse Filter Cartridges. Art pertinent to the subject matter of the present invention can be found in U.S. Patent Class 55.
Baghouses are employed to filter particulates from air expelled by various commercial processes. Some processes employ baghouses to remove hazardous wastes before venting to the atmosphere. Other processes use baghouses to gather output product.
Most modern baghouses employ a stainless steel skeletal framework, commonly referred to as a cage, to support filter bags. Together the cage and bag form a cartridge. Various mounting systems are used to anchor these cartridges in baghouse structures. Generally speaking, the cartridges are mounted to a tube sheet which is a flat plate with a plurality of cartridge receptive orifices defined in it. The cartridges may be clamped in place. Alternatively, a series of indents or notches defined in a flange around the opening mate with grooves or ribs defined in a shroud on the open end of the cage to hold the cartridge in place. The tube sheet is mounted in the baghouse in such a manner that it separates the input gases from the output gases. Gases to be filtered pass though the bags in one direction or the other, collecting material on the outside or the inside of the bag.
Innumerable patents are directed to baghouse configurations. Birkholz, U.S. Pat. No. 1,821,202, discloses a renewable capsule filter which employs a baghouse structure having a mesh frame. More conventional, modern baghouses are disclosed in several U.S. Patents Dobyns, U.S. Pat. No. 4,976,756, discloses a dust collector with a hinged roof to facilitate cleaning and use. Heffernan, U.S. Pat. No. 4,309,200, discloses a baghouse with a collapsible filter bag assembly.
Some U.S. Patents speak directly to filter structures and the connections employed to secure the cartridge to the tube sheet. De Martino, U.S. Pat. No. 4,256,473, discloses a cylindrical collar unit used to attach a bag frame to the permanent baghouse structure. Gravley, U.S. Pat. No. 3,937,621, discloses a filter bag cuff. It is basically a ring folded within the fabric of the bag and stitched into place. Reinauer, U.S. Pat. No. 4,073,632, discloses a structure for mounting bags. This structure uses a semirigid bag with an integral framework. This patent discloses two end caps, one which allows the entrance of air and the other which supports the distal end of the bag. Miller, U.S. Pat. No. 4,042,356, discloses a baghouse cell plate and filter bag attachment. Here a structure extends outward from the baghouse cell plate with a grove in it for accepting the upper lip of a filter bag. U.S. Pat. No. 4,424,070 issued to Robinson Jan. 3, 1984, discloses a dust collecting filter cartridge and attachment structure. The attachment structure is an adapter that uses a rubber clamp to mate dissimilarly sized cartridges and tube sheets.
U.S. Pat. No. 5,095,607 issued to Simon on Mar. 17, 1992, discloses a tool for securing baghouse filters. It employs a tapered head to expand the open end flange of a baghouse filter cartridge to facilitate inserting it into the tube sheet or other framework.
Various means are employed to clear the material from the bags in the baghouse. For example, Bundy, U.S. Pat. No. 4,113,449 discloses a two step process. First, the pressure of the gases flowing through the bags is reduced. Next the bags are blasted with high pressure gas to dislodge collected particles. Another method uses vibration. However, over time the bags become so heavily clogged with material that they must be replaced.
The first step in replacing the bags is removal of the cages mounting the filtration bags from the baghouse. Once removed from the baghouse, prior art methods for replacing bags require manually stripping or pulling the bags from the cages. Bent or damaged cages are generally discarded as scrap metal. This manual procedure has many drawbacks. For example, if the baghouse is intended to filter hazardous waste, the individuals stripping the bags are exposed directly to the waste in question. Therefore, cumbersome, expensive protective equipment is required. Additionally, cages are often bent during the stripping process. As a result, cages that would be perfectly serviceable, if a less forceful method was employed, are rendered scrap metal. Cages are also damaged when the new bags are installed. To manually install a bag requires that the cage be handled a great deal, risking bending the cage or breaking welds. Finally, possibly the greatest drawback is costs. The value of a cage as scrap metal, in comparison to the cost of a new cage, is minuscule. The manhours involved in this manual process are significant. Additionally, while the filter cartridges are removed the baghouse will not be operational. In some circumstances this can result in downtime for a significant portion if not an entire plant.
Hence, it is desirous to provide a process for replacing baghouse filter bags which strips the bag from the cage without damaging the cage. Additionally, it is desirous to straightening bent cages and to repair damaged cages, allowing continued use. For example, welds holding the cages together are often destroyed due to continual exposure to vibration in the baghouse. Welds may also be broken during removal from the bag house or during subsequent handling such as the aforementioned straightening procedure. Preferably the bags will be stripped from the cages in such a way that direct contact with materials captured in the bags will be avoided. Furthermore, it is desirous to suppress dispersion of the material in the bags into the air. Finally, it would be beneficial if the process could be carried out in such a manner that downtime was reduced as well as costs generally.